A-a Gradient or Alveolar-arterial PO2 difference – measure of the difference between the alveolar concentration (A) of oxygen and the arterial (a) concentration of oxygen. The A-a Gradient can help determine the cause of hypoxia.
- Assesment of oxygenation
- valid only on room air
- increase with age
Causes of increased (A-a) difference:
- Pulmonary edema
- Interstitial Lung disease
Increase in all cases of hypoxemia, except hypoventilation and high altitude.